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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2017/imperative-programming/5/c/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2017 / Imperative programming / 5 / c / Solution by

Codex  0 2026-10-31

The decorator pattern participants are:

Component: CableTV declares the common cost and packages queries, so clients can use both basic and decorated accounts through one object interface.
Concrete component: BasicPlan supplies the initial price and package description.
Decorator: the abstract Packages class stores a component reference and forwards its operations, enabling recursive object composition.
Concrete decorators: Movies and HDChannels override the queries to add one responsibility while preserving the wrapped component's behavior.
Client: an application chooses the nesting of components and observes the resulting account through CableTV.

Each wrapper contributes its price exactly once along the chain. The same structural arrangement handles a new optional package without changing the existing component interface.

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